The earth, for instance, has plenty of plane trees (6)
I believe the answer is:
planet
'the earth for instance' is the definition.
(Earth is an example)
'plane trees' is the wordplay.
'trees' becomes 't' (this could be a standard abbreviation I've not previously seen).
'plane'+'t'='PLANET'
'has plenty of' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for planet that I've seen before include "Heavenly (or earthly!) body" , "Heavenly body moving round the sun" , "Eg, Mars or Pluto" , "body in orbit" , "Mercury?" .)